Electroslag furnace eliminating magnetic stirring effect

ABSTRACT

An electroslag furnace is provided with a power connection equivalent to a coaxial conductor to eliminate the deleterious effects of magnetic fields upon the pool of molten metal.

Unite States tent [151 3,684,001 Weeding et al. [4 1 Aug. 15, 1972 1 ELECTROSLAG 1 i ACE References Cited ELIMINATING MAGNETIC S 1 f'i NG UNITED STATES PATENTS EFFECT 2,951,890 9/1960 Yeomans et a1. ..13/9 x [72] Inventors: Patrick J. W, Moorestown; 3,067,473 12/1962 Hopkins 164/52 Raymond John Roberts, Willing- 3,379,238 4/1968 Sieckman 164/52 X boro, both of NJ. 3,439,103 4/1969 Holzgruber et a1 ..164/252 UX [73] Assgnee' 3 cwpmmn Ranmas 3,510,562 5/1970 Frauenstein ..164/52 x 3,072,982 l/1963 Gordon et a1. ..75/10 C UX [22] Filed: May 11, 1970 3,476,171 11/1969 Stark et al. ..l64/52 [2]] Appl' Primary Examiner-R. Spencer Annear AttornqV-Seidel, Gonda & Goldhammer [52] U.S. CI ..l64/250, 75/10 C, 13/9,

13/12 [57] SCT [51] Int. Cl. ..B22d 27/02 An electrosla g furnace 1s provided with a power con- [58.] Field of Search 164/52 g ?6% nection equivalent to a coaxial conductor to eliminate the deleterious effects of magnetic fields upon the pool of molten metal.

10 Claims, 4 Drawing figures PAIENIEDAus 1 s 1912 snm 1 [1F 3 FIG.

INVENTORS. PATRICK J WOOD/N6 RAYMOND J. ROBERTS A TTOR/VE rs.

P'ATENTEDAUBISIIQYZ v 3584.001

SHEET 2 BF 3 m/ vg/vroRs. PATRICK J. WOOD/N6 RAYMOND J. ROBERTS ATTORNEY.

PAIENIEDAus 15 m2 SHEET 3 OF 3 IN VE N T 0R5 PATRICK J. WOOD/N6 RAYMOND J. ROBERTS A T TOR/V575.

ELECTROSLAG FURNACE ELIMINATING MAGNETIC STIRRING EFFECT This invention relates to a power connection for an electroslag furnace. More particularly this invention relates to a power connection which is the equivalent of a coaxial conductor so as to eliminate the various deleterious effects of magnetic fields.

The present invention relates principally to apparatus for distributing the current in an electroslag furnace to eliminate the stirring effects of the magnetic field on the pool of molten metal.

One of the primary advantages of consumable melting is the progressive solidification of the ingot. Thus the typical consumable electrode furnace first forms a pool of fused metal which enlarges to a determined volume and thereafter remains fairly constant while progressive solidification takes place at the bottom of the pool.

It is known that the shape of the interface between the liquid and solid metal at the top of the resulting ingot plays a very important part in determining the metallurgical quality of the ingot itself. In the electroslag process the operating conditions are chosen so that the solidification front obtained is as flat or horizontal as possible to promote the formation of an ingot of high quality.

Another factor which has been found to influence greatly the quality of the resultant ingot is the degree of stirring or agitation of the molten metal pool. It has been found that for many materials, particularly those with high alloy contents which are subject to alloy segregation, the most uniform ingot structure and the highest ingot quality are obtained when the molten metal pool is completely or almost completely quiescent.

In conventional electroslag furnaces as previously constructed, a quiescent molten metal pool has not been obtainable because of inherent magnetic stirring. This effect results from the inter-action between the horizontal components of the main process current which flow radially towards the sidewall of the crucible, and vertical components of stray magnetic fields produced by the various conductors used to carry current to and from the process. The stirring effect occurs on alternating current furnaces as well as on direct current furnaces because when AC is used the current and the stray magnetic fields reverse simultaneously and the direction of the motor force acting on the molten slag and metal pools remains the same.

There have been no known attempts to eliminate the effects of the magnetic fields in electroslag furnaces mainly because magnetic stirring was not thought to be a problem in electroslag processes. Even with the inherent stirring that occurs in conventional furnaces, the quality of the ingot produced is very high providing the correct operating conditions have been selected. It is however, one of the objects of the present invention to eliminate inherent stirring, resulting in an even higher ingot quality or alternatively resulting in the ability to obtain equivalent quality at a higher production rate.

The objects of the present invention are achieved by providing a coaxial conductor or the equivalent thereof for supplying power to an electroslag furnace. The purpose for using a coaxial conductor design can best be understood by analyzing the nature of the magnetic forces produced in a typical electroslag furnace. The

electrode which is to be melted in such a process must be smaller in diameter than the crucible which will contain the forming ingot and its associated molten slag and molten metal pool. When current is passed between the electrode and the ingot, this diameter difference inevitably results in horizontal components of current flowing radially outwards towards the perimeter of the mould or radially inward towards the electrode depending on the polarity of the applied voltage. In addition to this, the skin effect (for alternating current) is much more pronounced in the molten metal pool than in the slag pool, because of the difference in their electrical resistances. This means that the tendency of the alternating current to flow on the outside is much more pronounced in the molten metal pool than it is in the molten slag pool. Again, in flowing from the slag pool to the molten metal pool or vice versa, horizontal components of current are produced. In a conventional electroslag furnace the power connections to the top of the electrode and the base of the ingot form a large single turn inductive loop generating considerable magnetic fields. These fields generally have a pronounced vertical component in the region of the melt zone. This vertical component will react with the radial component of the electrode current to produce a circulatory motor force according to the classical left hand motor rule.

From the foregoing it is apparent that reducing the vertical component of magnetic field will reduce the deleterious stirring effects. This is accomplished by arranging that the current connection to the top of the electrode and the return conductor from the base of the ingot form a vertically orientated coaxial conductor.

It should be noted that in a conductor system which consists of a vertically orientated coaxial conductor, the magnetic field is completely confined to the space between the inner and outer conductors, and further, the orientation of this magnetic field is completely horizontal. There are no vertical components of field in such a system which could produce magnetic stirring in an electroslag process.

In practice it is difficult to achieve such an ideal coaxial condition because the electrode must be fed downward as it is consumed and because the necessity for access to the furnace prevents the use of a continuous outer return conductor normally associated with a coaxial connection.

In one embodiment of the present invention, displacement of the electrode is provided for, by the incorporation of a sliding contact system. A number of discrete conductors (preferably at least three) are used to obtain the effect of a coaxial return conductor. It has been found in practice that four or more conductors are required to give the same effect as a continuous return conductor but the use of three or even two conductors represents an improvement over the conventional system.

The confinement of the magnetic field previously mentioned results in a conductor system having an inductance much lower than that of a conventional electroslag furnace. This means, for furnaces operated with AC power, that the reactive voltage drop between power supply and the molten slag pool is relatively small and the furnace exhibits a relatively high operating power factor. A further advantage which occurs when sliding contacts are used, is that the length of the coaxial conductor remains fixed even though the electrode is being consumed or melted. This means that the reactive voltage drop is fixed for any particular current level. By contrast, in a conventional electroslag furnace the large single turn inductuve loop fonned by the power connection decreases in size as the electrode is melted. This results in a decrease in the reactive voltage drop as the process proceeds, thereby necessitating a controlled decrease in the output voltage of the power supply by way of compensation in order to maintain the thermal and electrical equilibrium of the melt zone. The elimination of this complication in the present invention therefore represents an additional advantage. Yet another advantage of the confinement of the magnetic field into the space between the inner and outer conductors of the equivalent coaxial system is the substantial elimination of the eddy current heating in the steel support structure of the furnace or adjacent equipment located outside the confined loop.

The object of the present invention, therefore, is directed to providing an electroslag furnace for use with alternating or direct current having the requisite equivalent of a coaxial conductor system to eliminate deleterious magnetic stirring of the molten slag and metal pools.

A further object of the present invention is directed to providing an electroslag furnace having the requisite equivalent of a coaxial conductor system which results in a high operating power factor when used with alternating current.

Yet another object of the present invention is directed to providing an AC electroslag furnace having the requisite equivalent of a coaxial conductor system of fixed length in which the reactive voltage drop remains substantially unchanged as the electrode is consumed.

A further object of the present invention is directed to providing an AC electroslag furnace having the equivalent of a coaxial conductor system which substantially eliminates eddy current heating of the steel support structure of the furnace and adjacent equipment.

The objects and advantages of the present invention are achieved by providing an electroslag furnace with a power connection equivalent to a coaxial conductor. This is accomplished by providing a return conductor extending substantially vertically from the base of the crucible. The return conductor, which is preferably a zone by the flexible conductors used to make an electrical connection between the coaxial configuration and the electrical power supply.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a side elevation view of the furnace with the head rotated out of alignment with the crucible.

FIG. 2 is a partial sectional view of the furnace showing an electrode and a partially fonned ingot within the furnace.

FIG. 3 is a plan view of the furnace illustrated in FIG. 1.

FIG. 4 is a partial sectional view of a second embodiment of the furnace.

The concepts of the present invention are best understood by referring 'to the drawings wherein like numerals designate like elements.

The drawings show a consumable electrode furnace of the electroslag type designated generally as 10. The furnace has been greatly simplified for purposes of describing this invention. Thus, such parts as the control console, slag feeder, and process starting equipment have not been shown since they form no part of the present invention. What is shown is an electroslag furnace having a crucible l2 resting upon a base 14. The crucible is fixed adjacent its top by a steel box frame 16. As best illustrated in FIG. 2, the crucible 12 includes an outer water jacket 18 for cooling the walls thereof. The crucible also includes an appropriate water cooled stool 20 at its base which is conventional in such crucibles. As indicated above, appropriate means (not shown) for inserting slag into the crucible are provided A furnace head 22 is reciprocably and rotatably supported above the crucible 12 by means of a large pin 24 extending through the head and fixed within an appropriate bearing 26 fixed to the block 28. The pin 24 also extends through a sleeve 30 which provides additional support for the furnace head 22. The block 28 and the sleeve 30 are supported by column 32. The pin 24 can be lifted by hydraulic cylinder 97 to provide reciprocal as well as rotational motion of the head 22.

A water cooled conductor34 is supported on the head 22 by hydraulic cylinders 36 which are fixed to the plate 38. Hydraulic cylinders 36 provide a means of rams 40 and 42 which are reciprocated by hydraulic pressure applied to pistons fixed at their ends within the cylinders 44 and 46. Thus, the water cooled conductor 34 can be reciprocated with respect to the head 22, and also the crucible 12, by appropriate control of the position of the rams 40 and 42.

The water cooled conductor 34 supplies current from one terminal of a power supply 200 to the electrode 50 to be remelted within the furnace. The electrode itself is supported at the end of the water cooled conductor by an electrode clamp 48. This is best illustrated in FIG. 2 wherein the electrode 50 is shown fixed in position on the clamp 48. Electric power is supplied to the water cooled conductor 34 by a sliding contact assembly 52 mounted within the head 22. The sliding contact assembly 52 is connected to a power supply 200 by a pair of water cooled conductors 54.

The electrical circuit from the power supply through the conductor 54, sliding contact assembly 52, water cooled conductor 34 and electrode 50 is completed through the pool of molten slag 98, the pool of molten metal 56, the ingot 53, the stool 20, and the return conductors 58, 60, 62 and 64. The partially formed ingot 53 is shown below the pool 56 in FIG. 2. Each of the return conductors 58-64 is divided into two sections. The first section is the lower or crucible section identified as 66, 68, 70 or 72. Each crucible section is electrically connected to the stool by means of appropriate connecting blocks 74, 76 and 78. The upper portion of each return conductor 58-64 is defined by one of the head sections 82, 84, 86 and 88. The upper or head sections of the return conductors are fixed within the head 22 and connected to a pair of water cooled conductors 90 which in turn are connected to the power supply.

The head sections of the return conductors are shown in FIG. 1 disconnected from the crucible sections so that the head 22 can be rotated out of alignment with the crucible 12. This is the position of the head 22 illustrated in FIG. 3. The head is rotated to the illustrated position so that a completed ingot can be removed from the crucible 12. This also permits removal and replacement of the crucible 12. After the ingot has been removed, a fresh electrode is positioned within the crucible and the head 22 thereafter rotated into position over the crucible 12. The electrode 50 is then fixed to the electrode clamp 48 so that it is properly aligned within the crucible. Thereafter, the head 22 is lowered so that each head section 82-88 mates with a corresponding crucible section 66-72 of the return conductors 5. This is illustrated in FIG. 2 wherein a male fitting 92 protruding from each of the head sections 82-88 is fitted within a cup-like female fitting 94 fixed to the end of the crucible section 66-72. Appropriate locking means 96 fix the fittings in mating relationship and provide good electrical contact. As thus fitted together, the sections of the return conductors 58-64 provide a return for completing the electrical circuit of the furnace 10.

The return conductors 58-64 are spaced at equal distances about the circumference of the crucible 12. Moreover, they extend upwardly parallel to the axis of the crucible 1'2 and are preferably kept as close to the crucible as possible. As thus positioned, they form the equivalent of the outer sheath of a coaxial cable. The water cooled conductor 34 and clamp 48 may be regarded as the internal concentric conductor. Also included in the internal conductor in an operating furnace are the molten slag pool 98, the molten metal pool 56, and ingot 53. The return conductors 58-64 provide a magnetic field which is equal and opposite to the magnetic field generated by the conductor 34, clamp 48, electrode 50, molten slag 98, molten metal 56, and ingot 53. Thus, the magnetic field external to the furnace is cancelled. Moreover, the coaxial positioning of the return conductors 5 to the internal concentric conductor (34, 48, 50, 98, 56, 53) eliminates all vertical components of magnetic flux and hence all stirring forces.

In the preferred embodiment four return conductors are provided. However, it should be noted that three conductors may suffice. Moreover, it may also be desirable to provide more than four return conductors. Four conductors, however, sufficiently control the magnetic field to provide the requisite equivalent of a coaxial configuration for all practical purposes.

As best illustrated in FIGS. 1 and 2, the coaxial effect is carried well above the melt zone 56 all the way into the head 22. It is only at the top of the head that conductors 54 and are displaced horizontally with respect to the furnace. Since the conductors 54 and 90 are kept close together, that is, they are laced their magnetic fields produced in the region of the melt zone are mutually cancelling. The net result is that there is very little reactive voltage drop in the circuit when AC power is used for melting. Indeed, a furnace constructed in accordance with the principles of this invention will have a much better power factor than other furnaces.

As previously indicated, the water cooled conductor 34 and electrode clamp 48 are used as a means to make electrical connection to the electrode 50. Power is supplied to the conductor 34 through the sliding contact 52. During the operation of the furnace, the foreshortening of the electrode 50 is taken up by the displacement of the conductor 34 downwardly toward and into the crucible 12. In view of the foregoing, the length of the current carrying internal conductor of the coaxial configuration does not decrease as the electrode 50 is melted. Since the length of the coaxial configuration remains fixed even though the electrode is being consumed, the reactive voltage drop in the entire circuit is fixed at any selected current level. Accordingly, there is no requirement for adjusting or compensating the power supply voltage to maintain thermal and electrical equilibrium in the melt zone.

Although the return conductors 58-64 define the preferred embodiment of the present invention, it

should also be noted that the crucible itself can be used as a return conductor as shown in FIG. 4.

In that Figure elements which are the same as those shown in FIG. 2 are identified by the same numeral. Hence the crucible 18 is electrically connected to the base 20' as well as to the head 22. The connection to the head may be by conductor means which are coaxial with the electrode 50'. The electrode 50' is connected to the power supply by conductors 54' and a sliding contact similar to contact 52 in FIG. 2. These conductors are electrically insulated from head 22'. The head 22 may be connected to the power supply by return conductors 90.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A power connection for an electroslag furnace, said furnace including a crucible, a crucible base, an electrode support and positioning means, and means to make connections to the electrode and the base from a power supply, the improvement comprising a return conductor electrically connected to the base, said return conductor being coaxially disposed around the crucible and the power connection to the electrode, the electrode, the molten slag pool, the molten metal pool, and the ingot to define a coaxial configuration, said coaxial configuration being continued to a point sufficiently above the molten slag and molten metal pools that negligible vertical components of magnetic fields will be generated in the melt zone by a conductor loop 7 used to make an electrical connection between the coaxial configuration and an electrical power supply.

2. A power connection in accordance with claim 1 rent-carrying coaxial configuration does not decrease as the electrode is melted.

' 5. A power connection in accordance with claim 4 wherein the power connection from the coaxial configuration to the power supply is laced.

7 6. A power connection in accordance with claim 4 wherein said return conductor comprises at least three discrete conductors substantially equally spacedabout the perimeter of the crucible.

A power connection for an electroslag furnace,

. said furnace including a crucible, acrucible base, an

electrode support and positioning means; a power supply, and means to make power connections to the electrode and the base, the improvement comprising a return conductor electrically connnected to the base,

said return conductor being coaxially disposed around the crucible and the power connection to the electrode, the electrode, the molten slag pool, the molten metal pool, and the ingot to define a coaxial configuration,

comprising three or more discrete conductors extending generally vertically upwards from said base, said conductors being equally spaced about the perimeter of said crucible, a separable head, said head supporting matching conductors defining a second conductor means to continue the return conductor vertically upwards to a first terminal point located on said head, means for connecting and disconnecting said second and a second terminal point insulated from said first terminal point, and laced, flexible powercables for making electrical connection between said terminal points and said power supply.

8. A power connection for an electroslagfumace in accordance with claim 7 wherein said firstterminal point is located on said head, and said second terminal point is positioned adjacent .to said first terminal point.

- the molten slag pool, the molten metal said return conductor including first conductor means conductormeans from said first conductor means so i that said head may be displaced to permit loading or 9. A power connection for an electroslag furnace in accordance with claim 7 whereinisaid sliding contact means is located on said head.

10. A power connection for anelectroslag furnace,

said furnace including a crucible, a crucible base, an

electrode support and positioning means, a power.

supply, and means to make power connections to the electrode and the base, the improvement comprising a return conductor electrically connected to the base, said return conductor being coaxially disposed around the-power connection to the electrode the electrode, e

pool, and th ingot to define a coaxial configuration therewith, said return conductor including the wall of said crucible extending generally vertically upward from said base,'a separable head, means for making and unmakingelectrical connection between said head and said crucible wall so that said head may be displaced to permit loading and unloading of crucibles, electrodes and ingots, said head defining a second conductor means to continue the return conductor vertically upwards to a first terminal point located on said head, said electrode support and positioning means passing through said head, sliding contact means for making an electrical connection between the electrode support means and a second tenninal point insulated from said first terminal point, and laced, flexible power cables for making electrical connection between said terminal points and said power supply. 

1. A power connection for an electroslag furnace, said furnace including a crucible, a crucible base, an electrode support and positioning means, and means to make connections to the electrode and the base from a power supply, the improvement comprising a return conductor electrically connected to the base, said return conductor being coaxially disposed around the crucible and the power connection to the electrode, the electrode, the molten slag pool, the molten metal pool, and the ingot to define a coaxial configuration, said coaxial configuration being continued to a point sufficiently above the molten slag and molten metal pools that negligible vertical components of magnetic fields will be generated in the melt zone by a conductor loop used to make an electrical connection between the coaxial configuration and an electrical power supply.
 2. A power connection in accordance with claim 1 wherein said return conductor comprises a number of discrete conductors.
 3. A power connection in accordance with claim 1 wherein said return conductor comprises at least three discrete conductors equally spaced around the perimeter of the crucible.
 4. A power connection in accordance with claim 1 including a sliding contact for making an electrical connection to an electrode, whereby the length of the current carrying coaxial configuration does not decrease as the electrode is melted.
 5. A power connection in accordance with claim 4 wherein the power connection from the coaxial configuration to the power supply is laced.
 6. A power connection in accordance with claim 4 wherein said return conductor comprises at least three discrete conductors substantially equally spaced about the perimeter of the crucible.
 7. A power connection for an electroslag furnace, said furnace including a crucible, a crucible base, an electrode support and positioning means; a power supply, and means to make power connections to the electrode and the base, the improvement comprising a return conductor electrically connnected to the base, said return conductor being coaxially disposed around the crucible and the power connection to the electrode, the electrode, the molten slag pool, the molten metal pool, and the ingot to define a coaxial configuration, said return conductor including first conductor means comprising three or more discrete conductors extending generally vertically upwards from said base, said conductors being equally spaced about the perimeter of said crucible, a separable head, said head supporting matching conductors defining a second conductor means to continue the return conductor vertically upwards to a first terminal point located on said head, means for connecting and disconnecting said second conductor means from said first conductor means so that said head may be displaced to permit loading or unloading of crucibles, electrodes and ingots, said electrode support and positioning means passing through said head, sliding contact means for making an electrical connection between the electrode support means and a second terminal point insulated from said first terminal point, and laced, flexible power cables for making electrical connection between said terminal points and said power supply.
 8. A power connection for an electroslag furnace in accordance with claim 7 wherein said first terminal point is located on said head, and said second terminal point is positioned adjacent to said first terminal point.
 9. A power connection for an electroslag furnace in accordance with claim 7 wherein said sliding contact means is located on said head.
 10. A power connection for an electroslag furnace, said furnace including a crucible, a crucible base, an electrode support and positioNing means, a power supply, and means to make power connections to the electrode and the base, the improvement comprising a return conductor electrically connected to the base, said return conductor being coaxially disposed around the power connection to the electrode, the electrode, the molten slag pool, the molten metal pool, and the ingot to define a coaxial configuration therewith, said return conductor including the wall of said crucible extending generally vertically upward from said base, a separable head, means for making and unmaking electrical connection between said head and said crucible wall so that said head may be displaced to permit loading and unloading of crucibles, electrodes and ingots, said head defining a second conductor means to continue the return conductor vertically upwards to a first terminal point located on said head, said electrode support and positioning means passing through said head, sliding contact means for making an electrical connection between the electrode support means and a second terminal point insulated from said first terminal point, and laced, flexible power cables for making electrical connection between said terminal points and said power supply. 